System and Method for Removing Particles From a Polishing Pad

ABSTRACT

A system for removing particles from a polishing pad to improve the efficiency of the removal of material by the polishing pad as part of a chemical-mechanical polishing process, the system comprising a polishing pad; a fluid dispenser arranged to dispense a fluid on the polishing pad; and removal means, wherein the removal means include a heater for increasing the temperature of the fluid dispensed on the polishing pad, and/or voltage means for coupling the polishing pad to a voltage source for repelling charged particles from the polishing pad surface while the fluid dispenser is dispensing the fluid on the polishing pad.

FIELD OF THE INVENTION

The present invention relates to system and method for removingparticles from a polishing pad to improve the efficiency of the removalof material by the polishing pad as part of a chemical-mechanicalpolishing process.

BACKGROUND OF THE INVENTION

Modern integrated circuit IC devices typically employ shallow trenchisolation and multi-level interconnects to meet the demands forincreased functionality and faster processing speeds. However,planarization of interlevel dielectrics, conductive layers and trenchdielectrics are required when using these technologies to obtain optimumfabrication results.

One technique that provides planarization and has received widespreadacceptance in the semiconductor processing industry ischemical-mechanical polishing CMP.

CMP is used to planarize and remove surface topography irregularities ofa material layer through chemical reaction and mechanical abrasion.

Typically a CMP process involves placing a substrate (e.g. asemiconductive wafer) face down on a polishing pad where the polishingpad is attached to a rotatable table, or platen. The polishing of thesubstrate by the polishing pad is normally performed with rotational,linear or orbital motion. Abrasive dispersions and chemical additives,known as slurry, are introduced onto the surface of the polishing padwhile the polishing pad is being rotated and the substrate is pressedagainst the polishing surface of the polishing surface of the polishingpad. Additionally, the substrate may also be rotated in conjunction withthe moving polishing pad.

The polishing of the substrate by the chemical-mechanical process isprovided by chemical interaction of the slurry, which includes chemicalreagents, with the substrate and abrasives contained within the slurry,where typical abrasives used in the CMP include silica, alumina andceria. However, other abrasives may be used.

The polishing process starts with the chemical interaction between theslurry and the substrate (i.e. material layer) with the abrasives in theslurry, coupled with the movement of the polishing pad relative to thesubstrate, removing the reacted surface material from the substrate. Thepolishing process continues until the desired amount of the materiallayer is removed. Upon completion of the polishing process the substrateis subjected to a cleaning process to remove residual slurry and foreignparticles.

However, by semiconductor fabrication standards CMP is inherently adirty process, which in addition to a significant amount of foreignparticles being introduced to the substrate surface also results in asignificant amount of foreign particles, for example abrasive particlesand by products of the planarization, being introduced to the polishingpad that can result in an undesirable built up of particles on thepolishing pad, which is an effect known as ‘pad glazing’.

Pad glazing results in the smoothing of the upper surface (i.e. workingsurface) of the polishing pad causing a reduction in the abrasiveproperties of the polishing pad and consequently a reduction in thepolishing rate.

Additionally, the ‘glaze’ is often unevenly distributed over a polishingpad surface, which can result in localized differences in polishing rateand increased polishing non-uniformity. Further, the foreign particlesattached to the polishing pad can result in increased wafer defectivitysuch as scratches and particle residues.

One way to alleviate this problem has been via the use of deionisedwater being dispensed on the polishing pad to aid in the washing off ofthe foreign particles, however this technique is largely ineffective.

Another solution that has been adopted to address this problem is theuse of a conditioning diamond disk that is used to remove the ‘glaze’and other unwanted particles from the polishing pad.

The technique of conditioning the polishing pad with a conditioningdevice involves mechanically abrading the polishing pad surface toremove the glaze and ‘renew’ the polishing pad surface.

However, it has been found that the conditioning of a polishing pad witha conditioning disk typically results in the foreign particles beingtransferred to the conditioning disk and as a result a film builds up onthe conditioning device and the conditioning capabilities of theconditioning disk are reduced resulting in a lower removal rate ofunwanted particles from the polishing pad by the conditioning device andless uniform conditioning of the polishing pad by the conditioningdevice.

It is desirable to improve this situation.

SUMMARY OF THE INVENTION

In accordance with an aspect of the present invention there is provideda system and method for removing particles from a polishing pad toimprove the efficiency of the removal of material by the polishing padas part of a chemical-mechanical polishing process according to theaccompanying claims.

This provides the advantage of improving the efficiency and cleanlinessof a polishing pad and for extending the life of the polishing pad,thereby extending the time before a polishing pad requires to bechanged. Additionally, by improving particle removal efficiency thiswill reduce defects in wafers polished by the polishing pad.

BRIEF DESCRIPTION OF THE DRAWINGS

An embodiment of the invention will now be described, by way of example,with reference to the drawings, of which:

FIG. 1 illustrates a top plan of a polishing pad conditioning system;

FIG. 2 illustrates a side view of a polishing pad conditioning systemaccording to a first embodiment;

FIG. 3 illustrates a side view of a polishing pad conditioning systemaccording to a second embodiment;

FIG. 4 illustrates a side view of a polishing pad conditioning systemaccording to a third embodiment.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIG. 1 illustrates a top plan of a polishing pad conditioning system 100that may be used in a chemical-mechanical polishing process.

The polishing pad conditioning system 100 includes a platen 101. Theplaten 101 is arranged to rotate clockwise or counter-clockwise about afixed or movable axis. A polishing pad 102 is attached to the platen 101and as such is rotated by the platen 101. The polishing pad 102 isarranged to provide mechanical abrasion for removing a material layerfrom a substrate (not shown) during a chemical-mechanical polishingprocess, as is well known to a person skilled in the art.

The polishing pad conditioning system 100 further includes an optionalconditioning device 103 having a conditioning arm 104 that is pivoted toallow the conditioning arm 104 to be disposed either away from thepolishing pad 102, as shown by dotted line, or above the polishing pad102. Attached to the conditioning arm 104, at the opposite end to thepivot, is a conditioning disk 105, for example a diamond disk. Theconditioning disk 105 includes a conditioning surface that duringconditioning of the polishing pad 102 is in abrasive contact with thepolishing pad 102, where the conditioning surface includes an abrasivesurface in order to facilitate removal of glaze that may be present onthe polishing pad 102. The abrasive surface will typically includeperiodic protrusions, for example diamonds, that extend partially intothe surface of the polishing pad 102 during the conditioning of thepolishing pad 102 by the conditioning device 103.

To aid the conditioning process the conditioning disk 105 may be rotatedin the same or opposite direction to that of the polishing pad 102. Theconditioning disk 105 may be swept back and forth along polishing pad,shown by arrows 106. Additionally, the conditioning disk may be movedfrom an inner portion of the polishing pad to an outer portion of thepolishing pad, as shown by arrow 107.

While the conditioning device 103 is not being used to condition thepolishing pad 102 the conditioning device 103 may be placed in a storageposition away from the polishing pad 102, as shown by the dotted linesin FIG. 1.

FIG. 2 illustrates a side view diagram of the pad conditioning system100 according to one embodiment of the present invention for removingparticles from the polishing pad 102, where the same features as thoseshown in FIG. 1 have the same reference numerals. Located above thepolishing pad 102 is a first conduit 200 that is arranged to dispense arinsing fluid, for example deionised water, and/or a chemical reagentonto the polishing pad 102 where typically the rinsing fluid alsocontains the chemical reagent. However, as would be appreciated by theperson skilled in the art, alternative designs for locating the firstconduit 200 could be adopted, for example a conduit could be integratedinto the conditioning device 103 for dispensing the rinsing fluid and/orchemical reagent. The chemical reagent is a chemical solution that issuitable to remove slurry by products such as ammonia, carboxylic acids(for example citric acid or commercially available chemicals such aselectraclean) or Ammonium hydroxide. Ideally the characteristics of thechemical reagent are chosen to have an appropriate pH and redoxpotential with reactive entities such as surfactant or ligand tosolubilize the generated polishing by-products disposed on the polishingpad 102, where the contaminants will depend upon the material beingpolished and the chemical used.

As also shown in FIG. 2, and as stated above, should the optionalconditioning device 103 form part of the polishing pad conditioningsystem the conditioning device 103 may be suspended in a storageposition away from the polishing pad 102, as shown by the dotted lines.

Coupled to the first conduit 200 is a heating element (not shown) thatis arranged to heat the rinsing fluid and/or chemical reagent as it isbeing dispensed on the polishing pad 102. Typically, the rinsing fluidand/or chemical reagent will be heated to a temperature between 25 and60 degrees Celsius. The purpose of dispensing the rinsing fluid and/orchemical reagent onto the polishing pad 102 is to reduce theaccumulation of previously used slurry and/or glaze present on thepolishing pad 102, where the inventors of the present invention haverecognised that heating the rinsing fluid and/or chemical reagentenhances this process.

Although the above description describes the heating of the rinsingfluid and/or chemical reagent as they are being dispensed on thepolishing pad 102 the rinsing fluid and/or chemical reagent could bearranged to be heated prior to being dispensed on the polishing pad 102,for example while the rinsing fluid and/or chemical reagent are beingkept in a storage reservoir (not shown). By increasing the temperatureof the rinsing fluid and/or chemical reagent this results in an increasein overall reaction kinetics such as complexation and solubilisation.

By heating the rinsing fluid and/or chemical reagent this has theadditional advantage of reducing rinsing fluid and/or chemicalconsumption as less fluid and/or chemicals are needed to solubilize byproducts of the polishing process. This is a consequence of theincreased temperature increasing the speed of solubilisation of theby-products, thus as less time is taken to solubilise by-products lesschemicals are required.

An additional or alternative method for conditioning the polishing padto that of heating the rinsing fluid and/or chemical reagent involvesthe use of ultrasonics or megasonics, which is illustrated in FIG. 3 inwhich the corresponding features to those shown in FIG. 1 and FIG. 2have the same reference numerals.

As shown in FIG. 3, in addition to the first conduit 200 being locatedabove the polishing pad 102 there is also mounted an acoustic nozzle 300arranged to emit a megasonic or ultrasonic wave at the polishing surfaceof the polishing pad 102 to aid in the removal of glaze and slurry buildup on the polishing surface, which is further assisted by the rinsingfluid and/or chemical reagent being dispensed on the polishing pad,which is ideally performed at the same time as the use of theultrasonics/megasonics. Any suitable ultrasonic or megasonic frequencyfor removing particles from the polishing pad may be used, however, apreferred frequency would be in the range of 0.7 to 1.2 MHz.Additionally, the power supply of the ultrasonics/megasonics willpreferably be in the range of 0.5 to 5 W/cm².

As would be appreciated by a person skilled in the art the acousticnozzle 300 could be mounted in a variety of different locations, forexample if a conditioning device forms part of the polishing padconditioning system the acoustic nozzle could be incorporated onto theconditioning device, thereby allowing megasonic energy to be applied tothe polishing pad as the conditioning disk is moved across the polishingpad. Additionally or alternatively the acoustic nozzle could be mountedbelow the polishing pad so that megasonic energy is applied through theplaten to the polishing pad and through the polishing pad to the fluidon the pad.

An additional or alternative method for conditioning the polishing padto that of heating the rinsing fluid and/or chemical reagent and/or theuse of megasonics involves the applying of a electrical potential to aconductive polishing pad as illustrated in FIG. 4 in which thecorresponding features to those shown in FIG. 1, FIGS. 2 and 3 have thesame reference numerals.

As shown in FIG. 4, in addition to the first conduit 200 being locatedabove the polishing pad 102 there is also coupled to the polishing pad102 a voltage source 400 for applying an electrical potential to thepolishing surface of the polishing pad 102 where, as stated above, thepolishing pad 102 is arranged to be conductive. Any suitable means forcoupling the polishing pad 102 to the voltage source 400 may be used.

Ideally, the electrical potential will be applied to the polishing padat the same time as the fluid is being dispensed on the polishing pad asthe chemicals in the fluid are designed to solubilize the by-products onthe polishing pad and the electrical potential prevents particlere-deposition.

The electrical potential applied to the polishing pad 102 will typicallybe in the range of 0.1 to 10 volts, however other voltages may be used.The voltage selected will typically depend on the particles to beremoved from the polishing pad 102 and the charge to be applied on it.

The polarity of the potential is ideally selected so that theelectrostatic force from the potential will result in a repulseinteraction between the particles and the adhering surfaces in therespective cleaning chemicals. During the conditioning process theby-product particles could be in contact with different surfaces, forexample polishing pad, conditioning disk, where these different surfacescan have different surface chemistries.

Further the polarity and the amplitude of the voltage could be changedduring the cleaning/conditioning cycle to ensure that the particles aresufficiently removed from all the surfaces.

In contrast, the use of chemicals alone involves significantly morecomplexity in the choice of appropriate chemicals to provide repulsiveforces between the particles of the by-products and the surfacesinvolved.

Another benefit of applying an external potential is that it cangenerate significantly higher repulsive force compared to the repulsiveforce generated by the surface chemistry of the particles. For example,the charges around the by-product particles in the hydrodynamic slippageplane are typically only in the order of 10 to 100 mV, the externalvoltage potential can be one to three orders of magnitude greater.

The electrical potential applied to the polishing pad 102 has the effectof repelling particles having an electrical charge with the samepolarity as the electrical potential being applied to the polishing pad102. Consequently, although a constant voltage source could be appliedto the polishing pad 102 it is a preferred embodiment for the electricalpotential to be alternated to allow differently charged particles to be‘lifted off’, from the surface of the polishing pad 102. The alternatingfrequency of the voltage potential would ideally be of the order of 0.1to 10 Hz. Further, specially designed ‘cleaning waveforms’ could beadopted, where the frequency of the alternating voltage being applied tothe polishing pad 102 is arranged to take into account the Zetapotential and density of the differently charged particles on thepolishing pad 102, where the zeta potential is the electrical potentialderived by the surface charges of the by-product particles and measuredin the hydrodynamic slippage plane of the particles in the respectiveelectrolyte.

The conditioning of the polishing pad 102 using the techniques describedabove will typically be performed for a predetermined period of time. Asthe conditioning of the polishing pad will typically not exceed the timeavailable during the production process the conditioning of thepolishing pad will typically occur for periods of 5 to 40 seconds.

It will be apparent to those skilled in the art that the disclosedsubject matter may be modified in numerous ways and may assumeembodiments other than the preferred forms specifically set out asdescribed above, for example the pad conditioning system may includemore than one polishing pad 102 and/or the optional conditioning device103 may be used in conjunction with one or more of the above describedprocesses for removing particles from a polishing pad.

1. A system for removing particles from a polishing pad to improve theefficiency of the removal of material by the polishing pad as part of achemical-mechanical polishing process, the system comprising: apolishing pad; a fluid dispenser (200) arranged to dispense a fluid onthe polishing pad (102); and at least one of the group consisting of aheater for increasing the temperature of the fluid dispensed on thepolishing pad while the polishing pad is polishing a substrate, and avoltage circuit for coupling the polishing pad to a voltage source forrepelling charged particles from the polishing pad surface while thefluid dispenser is dispensing the fluid on the polishing pad.
 2. Asystem according to claim 1, wherein the fluid dispenser is arranged todispense deionised water.
 3. A system according to claim 1, wherein thefluid dispenser is arranged to dispense a chemical reagent.
 4. A systemsaccording to claim 3, wherein the dispense chemical reagent is achemical suitable to remove slurry by products.
 5. A system according toclaim 1, further comprising an acoustic nozzle arranged to emit anultrasonic or megasonic signal at the polishing pad while the fluiddispenser is dispensing the fluid on the polishing pad.
 6. A systemaccording to claim 5, wherein the frequency of the megasonic is between0.7 to 1.2 MHz.
 7. A system according to claim 5, wherein the fluiddispenser is arranged to dispense fluid and the acoustic nozzle isarranged to emit a megasonic signal while the polishing pad is polishinga substrate.
 8. A system according to claim 16, wherein the voltagesource is arranged to alternate to allow opposite charged particles tobe removed from the polishing pad.
 9. A system according to claim 16,wherein the voltage source is between 0.1 and 10 volts.
 10. A systemaccording to claim 15, wherein the fluid is heated to a temperatureabove 25 degrees Celsius.
 11. A system according to claim 16, whereinthe polishing pad is arranged to be conductive.
 12. A method forremoving particles from a polishing pad to improve the efficiency of theremoval of material by the polishing pad as part of achemical-mechanical polishing process, the method comprising: dispensinga fluid on the polishing pad; and performing at least one of the groupconsisting of increasing the temperature of the fluid dispensed on thepolishing pad while the polishing pad is polishing a substrate, andcoupling the polishing pad to a voltage source for repelling chargedparticles from the polishing pad surface while dispensing the fluid onthe polishing pad.
 13. A system according to claim 2, wherein the fluiddispenser is arranged to dispense a chemical reagent.
 14. A systemaccording to claim 6, wherein the fluid dispenser is arranged todispense fluid and the acoustic nozzle is arranged to emit a megasonicsignal while the polishing pad is polishing a substrate.
 15. The systemof claim 1, wherein the system comprises the heater.
 16. The system ofclaim 1, wherein the system comprises a voltage circuit.
 17. The systemof claim 1, wherein the system includes both the heater and the voltagecircuit.
 18. The method of claim 12, wherein the method includes theincreasing the temperature.
 19. The method of claim 12, wherein themethod includes the coupling the polishing pad to the voltage source.20. The method of claim 12, wherein the method includes both theincreasing the temperature and the coupling the polishing pad to thevoltage source.